1. Field of the Invention
This invention relates to the use of silicon quantum dots in a surface emitting laser. More specifically, this invention relates to dynamic variation in the color produced by such a device.
2. Description of the Related Art
Quantum well lasers are known in the art. The use of quantum dots, or small volumes of semiconductor, leads to quantized energy states, resulting in narrow spectrum light. Some examples of patents in this field are U.S. Pat. No. 5,131,001 by Carlson, U.S. Pat. No. 5,103,456 by Scifres et al., U.S. Pat. No. 5,077,752 by Toda et al., U.S. Pat. No. 5,019,787 by Carlson et al., U.S. Pat. No. 4,976,539 by Carlson et al., and U.S. Pat. No. 4,815,087 by Hayashi. In general, a quantum well region is formed in an active layer between two opposite conductivity type semiconductor layers of a wider energy bandgap than the quantum well region. The light is made coherent by some means, such as a distributed feedback mechanism, which creates changes in the optical index periodically, with the period relating to the wavelength of the light. A grating is used to pick off the laser light which is propagating laterally within the active lasing layer.
Recent advances in the technique of producing the quantum dots within the active lasing layer have improved the quality and uniformity of the coherent light capable of being produced. "Transfer of Biologically Derived Nanometer-Scale Patterns to Smooth Substrates" by K. Douglas et al., Science, Vol. 257, 31 Jul. 1992, describes a procedure for producing quantum dots of extremely uniform size and spacing. The size of the dots is controllable by varying the particular protein used in the process described. Thus, it is possible, by selecting the size of the quantum wells, to change the frequency of the light generated by a quantum well device. However, no one until now has developed a mechanism for dynamically changing the color of light emitted from such a device, nor have they made uniformly sized quantum dots in silicon.